1. Field of the Invention
The present invention relates generally to the field of magnetic imaging. More specifically, the present invention relates to a magnetic resonance imaging coil designed to support the combination of a large imaging volume at high magnetic field strengths.
2. Description of the Related Art
The magnetic resonance phenomenon is a phenomenon in which atomic nuclei placed in a static magnetic field and having non-zero spins and magnetic moments absorb and emit electromagnetic-wave energy at specific resonant frequencies. The atomic nuclei are excited to resonance at the Larmor angular frequency given by .omega.o=.gamma.Ho, wherein .gamma. is the gyromagnetic ratio inherent in the atomic nuclei and Ho is the strength of the static magnetic field.
The apparatus adapted to make in vivo diagnosis utilizing the above principle performs signal processing on electromagnetic waves having the same frequency as above and induced after the resonance absorption, thereby obtaining diagnostic information of an object to be examined.
To acquire diagnostic information utilizing magnetic resonance, the whole body of a human subject placed in a static magnetic field may be excited to acquire magnetic resonance signals from the whole body. In view of constraints on construction of apparatus and clinical requirements for magnetic resonance images, however, actual apparatuses are adapted to excite a specific body region of the subject and acquire magnetic resonance signals from the body region.
A specific body region is generally defined by a radio-frequency (RF) magnetic field (a RF pulse) produced by a radio-frequency magnetic field producing coil and gradient magnetic fields produced by gradient magnetic field producing coils. The subject to be examined is placed within a radio-frequency coil system such as a saddle-shaped whole-body coil. The position and thickness of a selected slice for diagnosis are determined by a radio-frequency magnetic field (a RF pulse) produced by the whole-body coil and gradient magnetic fields Gx, Gy and Gz produced by gradient magnetic field producing coils. In this case, the spatial distribution of the radio-frequency magnetic field is determined by coil characteristics such as the coil pattern shape, the distribution and capacitances of distributed capacitors, as well as the conductivity and dielectric constant of the subject to be examined.
When a whole-body coil is used, non-uniformity will be produced in the radio-frequency magnetic field distribution because of the influence of the coil characteristics. In addition, the spatial distribution of radio-frequency magnetic field will be distorted (become non-uniform) within the subject because of its conductivity, permeability, and boundary condition depending on the radio-frequency magnetic field characteristics produced by the coil. These factors could produce irregularities in sensitivity in obtained MR images. For example, in a magnetic resonance imaging apparatus utilizing such a high magnetic field as 3 Tesla and greater, the propagation effects due to the short wavelength of the resonance frequency and other physical limitations of existing coil designs, prevents acquisition of MRI information.
Therefore, The prior art is deficient in the lack of effective apparatus/means of imaging large volume subject at high magnetic field strengths (xe2x89xa73 Tesla). The present invention fulfills this long-standing need and desire in the art.
The present invention is directed to a high frequency large volume resonator (HFLVR), which is an adaptation of a design intended for small volumes and high fields. A high frequency large volume resonator is a magnetic resonance imaging coil designed to support the combination of a large imaging volume at high magnetic field strengths of 3 Tesla and higher.
In one embodiment of the present invention, there is provided a magnetic resonance imaging coil, comprising a conductive cavity supported by an outer shell; a first transverse plane with hole structure, which is connected to the first end of the conductive cavity; a second transverse plane with hole structure, which is connected to the opposing end of the conductive cavity; and coaxial cables, wherein the cables are fed through the first transverse plane via the hole structure, through the conductive cavity of the HFLVR, and through the second transverse plane via the hole structure, and wherein the cables have an open end and an end opposing the open end, wherein the end opposing the open end is connected with a tuning network. Preferably, the coaxial cables within each pair are separated by 60xc2x0. Appropriate capacitive and inductive components may be substituted to simulate the open coaxial cables (stubs).
In another embodiment of the present invention, there is provided a linear mode magnetic resonance imaging coil, comprising a conductive cavity supported by an outer shell; a first transverse plane with four holes, which is connected to the first end of the conductive cavity; a second transverse plane with four holes, which is connected to the second end of the conductive cavity; and two pairs of coaxial cables, wherein the cables within each pair are separated by 60xc2x0 and the cable pairs are separated by 180xc2x0, and wherein the cables are fed through the first transverse plane via the holes, through the conductive cavity, and through the second transverse plane via the holes, and wherein each cable has an open end and an end opposing the open end, and wherein the open end of second pair cables is on the opposing end of the conductive cavity compared to the open end of first pair cables, and wherein the end opposing the open end of the first pair cables and the end opposing the open end of the second pair cables are connected with a tuning network. Alternatively, additional toroidal end rings may be attached to the outer shell to enclose the tuning and coaxial cable network.
In still another embodiment of the present invention, there is provided a quad mode magnetic resonance imaging coil, comprising a conductive cavity supported by an outer shell; a first transverse plane with eight holes, which is connected to the first end of the conductor; a second transverse plane with eight holes, which is connected to the second end of the conductor; and four pairs of coaxial cables, wherein each pair cables are separated by 60xc2x0 and the 4 pairs are separated by 90xc2x0. The coaxial cables are fed through the first transverse plane via the holes, through conductive cavity, and through the second toroidal transverse end plane via the holes, and wherein the each pair cables have an open end and an end opposing the open end, wherein the end opposing the open end are connected with a tuning network. Alternatively, additional toroidal end rings may be attached to the outer shell to enclose the tuning and coaxial cable network. Alternatively, additional toroidal end rings may be attached to the outer shell to enclose the tuning and coaxial cable network. Appropriate capacitive and inductive components may be substituted to simulate the open coaxial cables (stubs).
Further provided in the present invention are methods of imaging a subject of large volume by applying the magnetic resonance imaging coils disclosed herein to the subject in a magnetic field, thereby obtaining a magnetic resonance image. Preferably, the magnetic field has a strength of at least 3 Tesla. The subject is selected from the group consisting of a human body and an animal body.
Other and further aspects, features, and advantages of the present invention will be apparent from the following description of the presently preferred embodiments of the invention given for the purpose of disclosure.